Suspensions containing microfibrillated cellulose

ABSTRACT

A suspension of a finely divided material in a liquid suspending medium which swells cellulose, the suspension containing microfibrillated cellulose in an amount sufficient to produce a stable, homogeneous suspension. The finely divided material is a dense solid such as coal or sand.

This is a division of application Ser. No. 202,740 filed Oct. 31, 1980,now U.S. Pat. No. 4,374,702.

This invention relates to stable homogeneous suspensions containingmicrofibrillated cellulose.

In U.S. Pat. No. 4,374,702 which issued on a continuation of ourcopending application, Ser. No. 107,446, filed Dec. 26, 1979 and nowabandoned, there is disclosed a new type of cellulose, denominatedmicrofibrillated cellulose, distinguished from prior celluloses by avastly increased surface area, greater liquid absorption characteristicsand greater reactivity. The microfibrillated cellulose there disclosedis prepared by repeatedly passing a liquid suspension of fibrouscellulose through a high pressure homogenizer until the cellulosesuspension becomes substantially stable. The process converts thecellulose into microfibrillated cellulose without substantial chemicalchange.

It has been discovered that the aforementioned microfibrillatedcellulose has the unique capability of enhancing the homogeneity andstability of a wide variety of suspensions. The presence ofmicrofibrillated cellulose in suspensions of the type used in foods,cosmetics, pharmaceuticals and such industrial products as paints anddrilling muds has been found to confer a number of unusual propertycharacteristics on the resulting product. In some cases, suspensions maybe made which were not previously possible. The microfibrillatedcellulose may be formed in situ in the suspension in a single stageoperation by mixing fibrous cellulose with the ingredients of thesuspension and then passing the mixture through an homogenizer oralternatively, the microfibrillated cellulose may be separately preparedand added to the suspension after preparation.

Specifically, the invention involves a suspension of finely dividedmaterial in a liquid suspending medium which swells cellulose, thesuspension containing microfibrillated cellulose in an amount sufficientto produce a stable, homogeneous suspension. The suspension is preparedin situ by mixing together a liquid which swells cellulose, a finelydivided material suspended in said liquid and fibrous cellulose to forma liquid suspension and repeatedly passing the liquid suspension througha small diameter orifice in which the mixture is sujected to a pressuredrop of at least 3000 psi and a high velocity shearing action followedby a high velocity decelerating impact, the process of converting thecellulose into microfibrillated cellulose, the microfibrillatedcellulose being present in an amount sufficient to form a stablehomogeneous suspension of the liquid and suspended material.Alternatively, the suspension may be prepared by mixing together theliquid which swells cellulose, the finely divided material suspended inthe liquid and the separately prepared microfibrillated cellulose in anamount sufficient to form a stable, homogeneous suspension of the liquidand suspended material.

There is an obvious cost savings in preparing the microfibrillatedcellulose and the suspension in a single stage operation. In addition,there is also in certain instances a product advantage which results inthe use of the single stage technique. The use of this single stagetechnique in the preparation of certain food products is the subject ofU.S. Pat. No. 4,341,807 which issued on our copending application Ser.No. 202,741 filed of even date with the parent of the presentapplication. In certain products, the heat build-up that accompanies thefibrillation process is detrimental and for such heat sensitive systemsthe separate preparation of microfibrillated cellulose is necessary.

The term suspension as used herein is intended to include within itsscope, suspensions in which a finely divided solid, liquid or gas aremixed with, but undissolved in, a liquid. The term thus includes anemulsion in which a liquid is dispersed in a second immiscible liquid,and a foam in which a gas is entrapped in the liquid and stabilized.

The amount of microfibrillated cellulose used in preparing thesuspensions of the invention will vary considerably depending on thenature and intended use of the suspension. For example, it has beenfound that oil-in-water emulsions may be rendered stable with 1% byweight or less of microfibrillated cellulose. The properties of latexpaint suspensions are enhanced with as little as 0.25% ofmicrofibrillated cellulose while sand suspensions are stabilized withfrom 2 to 3% of microfibrillated cellulose. At the other extreme, themicrofibrillated cellulose may be present as the predominant or majoringredient of the suspension. In general, the microfibrillated celluloseshould be present in an amount sufficient to accomplish its function ofproducing a stable, homogeneous suspension. In most applications, thisamount will range from about 0.25% to about 5%, the percentages beingthe weight of cellulose solids present as microfibrillated cellulosebased on the total weight of the suspension.

The preparation of the microfibrillated cellulose, either in situ in thesuspension or separately, is assisted by the addition to the startingmixture of a hydrophilic polymer which may be cellulose ester or ether,a synthetic acid polymer (or copolymer), a natural gum or a starch.Examples of such hydrophilic polymers are carboxymethyl cellulose,methyl cellulose (methocel), hydroxypropyl cellulose, polyacrylic acid,carageenin and guar gum. Addition of the hydrophilic polymer to theliquid suspending medium, prior to cellulosic pulp addition, appears toprevent dewatering of the pulp (or other fibrous cellulose) under thehigh pressures of the fibrillation process and thus allows the slurry topass through the homogenizer at higher slurry concentrations. Moreover,the microfibrillated cellulose produced with the additive present alsodisplays improved freeze-thaw stability and improved dewateringresistance under pressure and thus produces improved suspensions inaccordance with the invention in those products where smoothness isimportant, as for example in hand creams, cosmetics and paints. Thehydrophilic polymer will enhance the fibrillation process at levels aslow as 0.1% by weight of the suspension, and may be used in amounts ashigh as 25%, depending on the nature of the suspension.

The following examples illustrate the practice of the invention. Unlessotherwise indicated, all parts and precentages are by weight.

EXAMPLE 1

A 4% cellulose slurry in approximately 3 gallons of water was preparedusing prehydrolyzed kraft pulp which had been cut to pass through a0.125 inch screen. The starting temperature of the slurry was 25° C. Theslurry was passed through a Manton-Gaulin (trademark) homogenizer at8000 lbs/sq. in. (gauge) ten consecutive times until a stable suspensionor gel-point was reached.

Microfibrillated cellulose can be used to adjust the rheology of paintto reduce dripping. In addition, the microfibrillated cellulose assistsin the coverage of the surface to be painted and thus reduces therequired levels of titanium dioxide pigment. This is illustrated byExamples 2-7.

EXAMPLES 2-7

The microfibrillated cellulose of Example 1 was added as a 4% slurry inwater to a commercial latex enamel white paint. A comparison of the driplength of the paint at various solid levels with and without variouspercentages of microfibrillated cellulose addition is set forth in TableI.

                  TABLE I                                                         ______________________________________                                                                                Drip                                                                          Length                                Example                                                                             % MFC    % Pigment % Solids                                                                             % Vehicle                                                                             (Inches)                              ______________________________________                                        2     0        15.97     15.97  84.03   8.8                                   3     0.25     15.72     15.97  84.03   8.2                                   4     0        15.34     15.34  84.66   8.5                                   5     0.50     14.84     15.34  84.66   6.0                                   6     0        14.06     14.06  85.93   12.0                                  7     1.0      13.06     14.06  85.93   4.0                                   ______________________________________                                    

It will be apparent from Table I that an amount of microfibrillatedcellulose as low as 0.25% reduces dripping of the paint and that at alevel of 1%, dripping as measured by drip length is one third of that ofan equivalent solids percent paint without microfibrillated cellulose.

Microfibrillated cellulose acts as a non-ionic emulsifying agent as wellas a stabilizer for emulsions. This is illustrated by the followingexamples.

EXAMPLES 8-16

A 4.7% solids microfibrillated cellulose slurry in water was prepared asin Example 1 from sulfite pulp. The slurry was then intimately mixedwith food grade soybean oil and additional water in a blender. Table IIsets forth the results of a series of experiments with and withoutmicrofibrillated cellulose and with various quantities ofmicrofibrillated cellulose, oil and added water to prepare anoil-in-water emulsion.

                                      TABLE II                                    __________________________________________________________________________         MFC Slurry                                                                           Oil Water Added                                                   Example                                                                            Grams  Grams                                                                             Grams  % MFC                                                                              % Oil                                                                             Result                                        __________________________________________________________________________    8    0      40  160    0    20  Stable emul-                                                                  sion not                                                                      possible                                      9    10.6   40  150    0.25 20  Stable emul-                                                                  sion not                                                                      possible                                      10   25     44  150    0.54 20  Stable emul-                                                                  sion not                                                                      possible                                      11   40     40  120    0.94 20  Stable                                                                        emulsion                                      12   40     80  80     0.94 40  Stable                                                                        emulsion                                      13   70     251 30     0.94 71.5                                                                              Stable                                                                        emulsion                                      14   50     64  51     1.42 38.8                                                                              Stable                                                                        emulsion                                      15   85     176 15     1.45 63.8                                                                              Stable                                                                        emulsion                                      16   85     100 15     2.0  50  Stable                                                                        emulsion                                      __________________________________________________________________________

It is apparent from the data in Table II that small amounts ofmicrofibrillated cellulose are able to stabilize emulsions containing upto 71.5% oil.

EXAMPLE 17

To demonstrate that stable emulsions can be made in situ (i.e. withoutseparate preparation of the microfibrillated cellulose), a 20% by weightstable emulsion was prepared from 80 grams of pulp which had been cut topass through a 0.125 inch screen, 800 grams of a liquid vegetable oil (afood grade oil sold under the trademark Crisco) and 3112 grams of water.The entire mixture was passed through an homogenizer at 8000 psig forten passes. The final emulsion contained about 2% microfibrillatedcellulose and was stable on the shelf at room temperature for at leastsix months.

Microfibrillated cellulose is also capable of use in relatively small,economical proportions for the preparation of stable emulsions of densesolids such as sand and coal for pipeline coal slurry pumping. Thefollowing examples demonstrate the usefulness of microfibrillatedcellulose for use as "packer fluids" of the type used for preventingsettling of suspended material during shutdown of drilling operations.

EXAMPLE 18

A 2% suspension in water of cellulosic pulp cut to pass through a 0.125inch screen was prepared as a control. To 100 grams of this suspensionwas added about 10 grams of ordinary sand. The mixture was shaken andallowed to stand. As expected, the sand settled rapidly to the bottom-nosuspending action was noted.

EXAMPLE 19

To a sample of 100 grams of a 2% slurry of microfibrillated cellulose inwater, about 10 grams of sand was added and the mixture was shaken. Uponstanding, the sand remained suspended for over three months. Unlike mostpolymeric thickened suspensions, the suspension was stable even ifheated to 100° C.

A second experiment was performed in which a layer of the sand wasplaced on top of a layer of the microfibrillated cellulose. Again, thesand did not settle through the microfibrillated cellulose and did notpenetrate it appreciably over a period of months.

Microfibrillated cellulose thus may be used at low concentrations (2 to3%) and therefore inexpensively in drilling operations and for enhancingthe stability of suspensions of relatively dense solids.

There is currently an active interest in the food industry in the use ofgums, or other substitute for oil, to produce "no-oil" salad dressings.It has been found that microfibrillated cellulose may be substituted foroil to produce a low calorie salad dressing. The product obtained frommixing a commercial Italian dressing mix yields a stable suspension ofspices which are uniformly distributed throughout the mix. A commercialThousand Island mix with microfibrillated cellulose yields a creamystable suspension similar to the texture of its oil base counterpart.Commercial preparations of Italian salad dressings generally requireshaking before use. The corresponding product made with microfibrillatedcellulose does not.

EXAMPLE 20

A vinegar solution was approximated by preparing a 5% (V/V) acetic acidsolution. Fifty-five milliliters of this vinegar was added to 25 ml ofwater in a cruet. In place of oil, 150 ml of a 1.7% microfibrillatedcellulose was substituted. An envelope of dried Italian salad mix wasadded and the entire mixture well shaken. A stable dispersion of thespices resulted. The color and texture of the material resembled veryclosely an authentic Italian dressing.

For comparison purposes, the equivalent amount (2.60 grams) ofcellulosic sulfite pulp, cut to pass through a 0.125 inch screen, wasadded to the same composition in place of microfibrillated cellulose.The cellulosic pulp quickly settled and did not suspend the spices.

EXAMPLE 21

A commercially available dry Thousand Island dressing mix was added toapproximately 225 ml of a 2% slurry in water of microfibrillatedcellulose and mixed well. A smooth consistency was obtained whichappeared quite similar to a regular Thousand Island dressing. Thesuspension was stable to settling.

The following examples illustrate further uses of microfibrillatedcellulose as an aid for emulsifying oils or fats in foods.

EXAMPLE 22

A 2% microfibrillated cellulose slurry was added to a ground porksausage mixture in an amount equal to 0.2% total cellulose based onfinal product weight. Upon frying, there was considerably less shrinkageof the sausage link and far less fat rendered as compared to the sameground mixture with no added microfibrillated cellulose.

EXAMPLE 23

A 2.5% microfibrillated cellulose slurry in water was added in theproportion of 1/3 slurry by weight to 2/3 by weight of ground chuckhamburger. This results in a product having 0.83% added cellulose basedon final product weight i.e. 27 g of hamburger, 12.67 g added H₂ O and0.33 g of cellulose. On cooking the product remaining weighed 24 g orthere was only a 3 gram loss from the original 27 g of hamburger whichcomes to an 11% weight loss on frying. By comparison a control weighing40 grams ended up at 26 g after identical frying conditions whichcorresponds to a 34% weight loss. Not only did the hamburger containingmicrofibrillated cellulose lose less weight, but it was far juicier anddid not have the extremely mealy taste of the control. Thus, addition ofthe 0.83% cellulose as microfibrillated cellulose served both to reducecooking losses and to improve overall taste and acceptance of the finalproduct.

EXAMPLE 24

A 2% microfibrillated cellulose slurry in water was added to acommercial meat emulsion used for making hot dogs in an amount equal to2% cellulose based on total weight of product. After stuffing, smokingand cooking the resultant wieners had a juicier taste and an improvedsmoke flavor retention as compared with an equivalent wiener withoutmicrofibrillated cellulose. Further, there is considerably lessformation of fat globules throughout the final product. Palate responsewas excellent.

EXAMPLE 25

Example 24 was repeated using a commercial bologna emulsion with 3%cellulose based on final product. As compared with the same bolognawithout microfibrillated cellulose, the resulting bologna has vastlyimproved response to lowered formation of fat pockets which is one ofthe major problems in the industry. The product was also juicier and hadbetter flavor retention than the control.

EXAMPLE 26

A low calorie whipped dessert topping was made by mixing together 2.2%cellulosic pulp, 6% sugar, 8% soybean oil and 83.8% water. The mixedingredients formed a slurry which was passed through an homogenizerhaving an 8000 psig pressure for ten passes. A whipped topping wasproduced with a smooth, consistent texture. The topping may, but neednot be, further whipped in a blender.

In the cosmetics industry, particularly in the area of skin care, a fewbasic materials are incorporated into different oil based formulations.The most common of these materials are glycerine and propylene glycolwhich are used as moisturizing ingredients. When microfibrillatedcellulose is produced in glycerol or propylene glycol sufficient body isimparted to the moisturizer so that expensive oils are not required.This not only lowers the costs, but also is an advantage for controllingoily skin. The translucent glycerine-cellulose (MFC) and propyleneglycol-cellulose (MFC) give a stable suspension of smooth consistencyquite like a commercial hand cream. The high absorbency of themicrofibrillated cellulose may additionally be used to carry otheragents as a slow release vehicle. The other agents may be bacteriostatsor other special skin care agents.

EXAMPLE 27

A 2% slurry of cellulosic pulp in glycerine was passed through aManton-Gaulin homogenizer for 950 seconds at 8000 psig for 12 passes toa final temperature of 135° C. The result was a stable suspension ofsmooth consistency quite similar to a commercial hand cream. To thissuspension base may be added various aroma contributing ingredients,lanolin, other softening oils, cleansing agents or bacteriocides asdesired.

EXAMPLE 28

Example 27 was repeated, using however propylene glycol as the liquidcarrier. The resulting product was similar to the glycerine basedproduct.

EXAMPLE 29

A 2% slurry of fluffed sulfite pulp in water containing 0.5% sodiumcarboxymethyl cellulose was passed through the homogenizer at 8000 psigfor 600 seconds or 10 passes to a final temperature of 100° C. A thickopaque paste was obtained which had an excellent consistency forcosmetic cream based uses, showing that water can also be used inaddition to glycols. Various aroma contributing ingredients, lanolin,other softening oils, cleansing agents or bacteriocides may be added tothis base as in Example 27.

The microfibrillated cellulose useful in the invention is morespecifically defined as cellulose having a water retention value over280%, a settling volume after 60 minutes in a 0.5% by weight suspensionin water of greater than 60% and a rate of degradation increase byhydrolysis at 60° C. in one molar hydrochloric acid at least twice asgreat as cellulose beaten to a Canadian Standard Freeness value of 50ml. Further and more detailed information concerning microfibrillatedcellulose, as well as its preparation, may be found in our aforesaidcopending application Ser. No. 107,446, the disclosure of which ishereby incorporated by reference.

We claim:
 1. A suspension of a finely divided dense solid selected fromthe group consisting of sand and coal material in a liquid suspendingmedium which swells cellulose, said suspension containingmicrofibrillated cellulose in an amount sufficient to produce a stable,homogeneous suspension.
 2. The suspension of claim 1 in which themicrofibrillated cellulose is present in an amount ranging from 0.25% tothe major ingredient of the suspension, said proportions being based onthe weight of cellulose solids present as microfibrillated cellulose ascompared to the total weight of the suspension.
 3. The suspension ofclaim 1 in which the dense solid is sand.
 4. The suspension of claim 1in which the dense solid is coal.